1. Field of the Invention
This invention is directed to systems and methods for ejecting or depositing substances containing multiple photoinitiators.
2. Description of Related Art
Direct marking print technologies are often limited by the time necessary to dry or cure the particular material that is being printed. For example, the ink drying inadequacies associated with ink jet-type printing have resulted in a limited number of applications for printing by this method. Printing by this method is seen most frequently in slow desktop printers. Once a water-based substance used in printing is applied to a substrate, such as paper, the ink remains wet until air dried or heat dried. In applications where double-side printing is required, or where printing is performed on non-absorbent substrates, the slow dry time is an obstacle to high print speeds. Slow dry time also limits speed and quality when printing with several different substances, or with the same substance on opposite sides of a substrate. For example, when different colored inks are deposited adjacent to each other, lateral bleed of the wet ink can reduce precision in graphics printing and other color printing applications. Similarly, second side relative registration is disturbed by wetness-induced media distortion.
A new printing technology exists that increases printing speed with fast, controllable drying ultraviolet photosensitive resin-containing substances. Fast drying substances containing ultraviolet photosensitive resins work well with direct marking print technology near room temperature.
The lithography industry is rapidly switching over to ultraviolet curable inks and pastes to take advantage of the fast drying nature of ultraviolet photosensitive inks on various substrates. However, the ultraviolet photosensitive substances used in lithography presses tend to have high tack or viscosity. Such formulations will not work with conventional ink jet technology. To use ultraviolet photosensitive inks in inkjet printing, an ink formulation having a low viscosity is required. Such formulations are known to those skilled in the art and can be manufactured using ultraviolet photosensitive resins typically used in the liquid crystal display industry.
With direct marking print technologies, such as ink jet applications, drop diameter spread control directly impacts the quality of print image resolution. To minimize lateral ink spread, the drop volume needs to be controlled and minimized, generally by using various ink delivery technologies. Properly selecting the target media substrate is also important. For example, cut-sheet paper tends to absorb water-based ink vertically and laterally, i.e., into and along the surface of the sheet. Furthermore, for printing on non-absorbing and semi-absorbing substrates, like transparencies, slow drying liquids, such as water based inks, will stay fluid and be held by surface tension until dried. These undried liquid puddles tend to smear if touched before they are completely dried.
In direct marking ejection or deposition methods, such as inkjet printing, the properties of the substances being ejected or ink being deposited are beneficially different at different stages of the process. For example, in the ejection head of a fluid ejection system, low viscosity is desirable, so that the fluid, such as ink, can be readily transported within the fluid distribution system and deposited onto a substrate. For a brief time after an ejected fluid droplet hits the substrate, a medium viscosity is desirable to allow intimate bonding of the fluid to the substrate, such as ink to the fibers of a sheet of paper, in a controlled fashion. However, quickly thereafter it is desirable that the fluid becomes rigid, to avoid lateral bleed. Curing substances containing ultraviolet photosensitive resins with conventional ultraviolet illumination, such as with a lamp or electron beam, makes it difficult to obtain and control the two separate phases of the substance that follow deposit on a substrate as described above.
Uncontrolled lateral spread of ejected fluids used in fluid ejection systems can be reduced and controlled by using fluids containing ultraviolet photosensitive resins. The quick-solidifying or xe2x80x9ccuringxe2x80x9d nature of such fluids eliminates the problems of uncontrolled lateral spread and slow drying of ejected fluids. Due to the fast-curing nature of fluids containing these resins, such as ultraviolet photosensitive resin ink, this fluid ejecting method is extendible to ejecting fluids onto any substrate. Substrates can include paper, in direct marking processes, or intermediate transfer belts or rollers, in non-direct printing processes. Ultraviolet light intensity and exposure time duration can provide control over lateral spread, by permitting the partial curing of a fluid containing an ultraviolet photosensitive resin.
Curing fluids or other substances, such as inks, containing ultraviolet photosensitive resins, is often accomplished using an electron beam or an ultraviolet lamp. Such methods of curing an ultraviolet photosensitive resin are deficient, because, for example, the ultraviolet lamp emits broad ranges of frequencies and wavelengths of ultraviolet light, and are thus only suitable for curing ultraviolet photosensitive resins that react to broad ranges of wavelengths of ultraviolet light. Such methods are also limited in their applications, due to considerations of portability, power consumption, and ability to achieve a small form factor.
This invention provides methods and systems for ejecting or depositing substances containing multiple photoinitiators.
This invention separately provides methods and systems for ejecting or depositing substances containing multiple photoinitiators, and separately subjecting the substance to illumination with wavelengths of light specific to the constituent photoinitiators.
This invention separately provides methods and systems that permit selective irradiation of multiple substances that are sensitive to distinct wavelengths of ultraviolet light.
Fluid ejecting or depositing with substances comprising multiple ultraviolet photoinitiators allows discrete changes in fluid viscosity. Rapid changes to a pre-determined state can be caused by irradiating the substance with amounts of light in excess of a saturation dose specific to one of the constituent photoinitiators to cause that photoinitiators to completely react. With multiple photoinitiators and processes requiring only short range diffusion, multiple initiators using different wavelengths can be used to change properties of the substances in discrete steps. This eliminates problems of variability in continuous processes where parameters must be tightly controlled.
According to various exemplary embodiments of the systems and methods according to this invention, ejection or deposition is conducted using fluids, or other substances, containing multiple photoinitiators so that super-saturation doses of radiation of wavelengths corresponding to each photoinitiator rapidly change the fluid to pre-defined new states. Thus, a first light flash, or a first spatial zone through which the substance passes, causes the substance to take on a first state dictated by the first photoinitiator in response to exposure to light having a wavelength that the first photoinitiator in the substance is sensitive to. Subsequently, a second flash, or a second spatial zone, having a wavelength corresponding to a second photoinitiator causes the substance to take on a second state dictated by the second photoinitiator. For example, exposing an ink comprising a first photosensitive resin and a second photosensitive resin to light of a particular wavelength can cause the ink to become immediately viscous enough to take on a certain diffusivity. Exposing the ink to a second light of a different wavelength can cause the ink to become rigid and fixed. Any excess amount of light does nothing more to the ink, because performing each discrete step consumes all of the particular photoinitiator.
In various exemplary embodiments, in which different intermediate steps are desired, various changes can be chosen. Sub-saturation irradiation can be used to create a lower viscosity for ejecting or depositing on particular substrates. Similarly, by having several photoinitiators in a substance, successive illumination with light having successive wavelengths can tailor the time evolution of the states associated with the photoinitiators. By implementing intermediate wavelength pulses of light, intermediate states can be effected.
While manipulating viscosity in ejected or deposited fluid is a useful application of the methods and systems of this invention, properties other than viscosity can be modified in similar ways. The applications are limited only by the capabilities of the photoinitiators that are employed. For example, the color of a substance could be manipulated after deposit.
These and other features and advantages of this invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of the systems and methods according to this invention.